Screw manufacturing method, whirling cutter, and screw manufacturing machine

ABSTRACT

A screw manufacturing method by thread whirling machining and others are provided which can solve problems due to thread rolling and cutting and which inhibits moving paths of inserts from interfering with a curved line of a desired screw upon going in and out, thereby providing the screw with a targeted curved line. In the method of manufacturing a screw, a mount angle of the screw is calculated by formulae below in case that a lead angle of the screw is different from the mount angle. 
       mount angle=tan −1   {n ×pitch/(π× D 1)}  (1)
 
         D 1={(screw valley diameter+screw outer diameter)/2}+Δ T   (2)
 
       screw valley diameter≦ D 1≦screw outer diameter  (3)
         in case ΔT&gt;0,       

       {(screw outer diameter−screw valley diameter)/2}×0.2&lt;Δ T &lt;{(screw outer diameter−screw valley diameter)/2}  (4)
         in case ΔT&lt;0,       

       −{(screw outer diameter−screw valley diameter)/2}&lt;Δ T &lt;−{(screw outer diameter−screw valley diameter)/2}×0.2  (5)
         where D 1 ≠0, ΔT≠0, and n indicates a number of threads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2009-294915 filed Dec. 25, 2009 in the Japan Patent Office, the wholedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a screw manufacturing method by athread whirling method, and a whirling cutter and a screw manufacturingmachine used in the thread whirling method. Accordingly, the presentinvention can be applied to a field of manufacturing ordinary screws,such as medical screws, worm screws, metric screw threads, and others.

BACKGROUND ART

A conventionally known method of manufacturing ordinary screws(mechanical screws) is, for example, thread rolling. In thread rolling,thread rolling dies corresponding to a specific screw-thread shape areused. Thus, thread rolling is preferred in the case of manufacturing amass of single products.

Other than thread rolling, a screw manufacturing method by turning isknown. In the method by turning, a work piece being rotated is cut by aturning tool. Turning is preferred in the case of manufacturing a widevariety of products in small quantities.

Separately from these screw manufacturing methods, a thread whirlingmachining is known as a manufacturing method of medical screws such asimplant screws and bone screws, for example (see Patent Document 1).

The thread whirling machining is a screw manufacturing method which usesan annular whirling cutter that is fixed to a tool spindle of a latheand is rotatable around its rotation axis, and a main spindle that holdsa rod to be machined (work piece) which is a material for manufacturinga screw and is rotatable.

In detail, the machining method uses a whirling cutter in which aplurality of inserts are radially arranged. A work piece held by themain spindle is inserted into a center through hole of the whirlingcutter. Also, the whirling cutter is inclined at a predetermined angle(mount angle) with respect to a center axis of the work piece. In thisstate, the work piece is moved forward in an axial direction while beingrotated in a predetermined direction. At the same time, the whirlingcutter is rotated at a rotation speed higher than a rotation speed ofthe work piece, thereby cutting a thread by one or a plurality ofinserts.

The mount angle set upon the above-described thread whirling machininghas been generally set equal to a lead angle in a design drawing of ascrew.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: U.S. Pat. No. 6,877,934

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In case that screws are manufactured by the above-described threadrolling, thread rolling dies corresponding to a specific screw-threadshape are used. Thus, thread rolling is not adequate to manufacturing ofa wide variety of products in small quantities.

Also, in case that screws are manufactured by turning, the turning isperformed by a turning tool. Due to a cutting load, it is difficult tocut a screw thread in one pass. The screw thread is formed in aplurality of passes. Thus, the machining requires time. Especially in acase of manufacturing a long screw, it is difficult to do the cuttingwork piece at a time. It is necessary to form the screw thread in asequential manner of, after forming several threads, forming anotherseveral threads, for example. Since the machining includes joining,there is a problem that machining accuracy at a joined part is low.

Further, in the case of medical screws, as compared to screws used inordinary machines, there are exceptional circumstances such that adifference between a valley diameter and an outer diameter is large, ashape of the screw thread is special (cross-sectional shape isorthogonal to a direction of a series of threads), etc. Thus, uponmachining of medical screws, a problem as below exists.

Particularly, as noted above, if a mount angle in thread whirlingmachining is set equal to a lead angle, it has been difficult tomanufacture a screw of a desired shape, depending on a targeted workpiece shape (screw-thread shape).

The first reason why it is difficult to obtain the targeted screw-threadshape is because medical screws have special shapes. The second reasonis because, since thread whirling machining is a machining method by amilling tool in which inserts are attached toward a center of a whirlingcutter and the whirling cutter rotates, moving paths (machining paths)of the inserts interfere with a curved line of a screw. That is, theinserts may shave a portion which should not be ground when going in andout of the work piece.

In other words, the problem is that shaving is performed in both inwardand outward cutting (as shown in FIG. 23, there are triangular grayzones (=interfering portions) in both an outer diameter side and avalley side of a screw). That is, if interference occurs to bothportions on the screw outer diameter side and the base end side (valleyside), it becomes difficult to fasten the screw with good accuracy.Further, backlash of the screw may occur.

However, if the interference occurs to either of the portions on thescrew outer diameter side or the screw base end side (valley side),there is not much problem in using the manufactured screw.

The problem due to the above noted interference is significantlyexhibited when a screw having a special shape such as a medical screw ismanufactured. The same problem may sometimes occur to other ordinaryscrews.

The present invention was made in view of the above problem. One objectof the present invention is to provide a screw manufacturing method bythread whirling machining, and a whirling cutter and a screwmanufacturing machine used in thread whirling machining, wherein theproblem due to thread rolling and turning can be solved. In the presentinvention, moving paths of the inserts are inhibited from interferingwith a desired curved line of a screw upon both going in and out.Thereby, a targeted curved line of a screw is provided in a preferredmanner.

Means to Solve the Problems

A first aspect of the present invention in order to achieve the aboveobject provides a screw manufacturing method for manufacturing a medicalscrew. The method uses: an annular cutter member (e.g., whirling cutter)that has a plurality of inserts radially arranged and is rotatable onits rotation axis; and a holding portion (e.g., main spindle) that holdsa work piece for forming the medical screw and is rotatable. The cuttermember is inclined with respect to an axial center of the work piece ata predetermined angle (mount angle). When a lead angle of the medicalscrew is different from the mount angle, the mount angle is calculatedby formulae (1), (2), (3), (4) and (5) below.

mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

-   -   in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4)

-   -   in case ΔT<0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5)

where D1≠0, ΔT≠0, and n indicates a number of threads.

In the screw manufacturing method of the present invention, even if alead angle of a medical screw, for example, is designed to satisfy aformula (X) below or the medical screw has a special shape specific tomedical screws, it becomes difficult for inserts to interfere with themedical screw upon rotating the work piece and the cutter member, asshown in TABLES 1 to 3 of later-explained first to third embodiments.

Particularly, if the mount angle is set smaller (shallower) than thelead angle (i.e., 0<ΔT), it becomes difficult to hit especially a sideface of a tip end of the screw thread. Conversely, if the mount angle isset larger (deeper) than the lead angle (i.e., 0>ΔT), it becomesdifficult to hit especially to a side face of a base end of the screwthread. Here, ΔT indicates an adjustment range of the mount angle.

Hereinafter, the above-described respective formulae will be explained.

As shown in the above formula (3), a minimum value of D1 is the screwvalley diameter, and a maximum value thereof is the screw outerdiameter. As shown in the formula (2), when D1=the screw valleydiameter, ΔT={(screw valley diameter)−{screw valley diameter+screw outerdiameter)/2}. Similarly, when D1=the screw outer diameter, ΔT={(screwouter diameter)−{screw valley diameter+screw outer diameter)/2}.Accordingly, when D1 is equal to the screw valley diameter or the screwouter diameter, the fluctuation range ΔT with respect to {screw valleydiameter+screw outer diameter)/2} takes a maximum value (also referredto as a maximum fluctuation range).

Here in D1, explanation will be given on a value of D1 between theminimum value and a pitch diameter, and the value of D1 between thepitch diameter and the maximum value.

By setting the fluctuation to 100% when ΔT=maximum fluctuation range,values of ΔT in fluctuations from 0 to 100% can be calculated.Particularly, when the fluctuation is 50%, ΔT=maximum fluctuationrange/2. The values of ΔT determined as such are given to the aboveformula (2) so that the value of D1 between the minimum value and thepitch diameter, and the value of D1 between the pitch diameter and themaximum value can be determined. By providing the acquired D1 to theabove formula (1), the mount angle can be calculated.

Further, as shown in TABLES 1 to 3 of the later-explained first to thirdembodiments, by setting the range of ΔT to the above formulae (4) and(5), it becomes difficult for the inserts to interfere with the medicalscrew.

lead angle=tan⁻¹ {n×pitch/(n×pitch diameter)}  (X)

-   -   where the pitch diameter={screw valley diameter+screw outer        diameter)/2}, and n indicates a number of threads.

Here, “n×pitch(P)” is a value called a lead (L), which is a distance ofmove when the screw is rotated once. The pitch diameter (D) is definedby JIS B0101 1215, the lead angle is defined by JIS B0101 1208, and thepitch is defined by JIS B0101 1206. Other terms also indicate meaningsdefined by JIS, respectively. Using the pitch diameter in calculation ofa lead angle is general to a person skilled in the art (the same appliesto below).

According to the present invention, moving paths of the inserts areinhibited from interfering with a desired curved line of a screw uponboth going in and out. Thereby, the screw provided with a targetedcurved line can be manufactured in a preferred manner.

Particularly, in the present invention, the interference can beinhibited from occurring to both the portions on the outer side of thescrew and the base end side (valley side) of the screw. Thus, uponfastening, etc., using the manufactured screw, the screw can be rotatedwithout problem. That is, there is no big problem in using themanufactured screw.

Here, the interference upon going in means the interference when theinsert enters the curved line of a screw, and the interference upongoing out means the interference when the insert goes out of the curvedline of the screw, upon machining the screw.

Also in the present invention, as compared to thread rolling, a widevariety of products in small quantities can be easily manufactured.Moreover, as compared to turning, machining time can be shortened. Also,continuous machining can be applied to one piece of work piece. Thus, ajoining process is not necessary. Machining accuracy is advantageouslyhigh.

-   -   A second aspect of the present invention provides a screw        manufacturing method for manufacturing a worm screw. The method        uses: an annular cutter member that has a plurality of inserts        radially arranged and is rotatable on its rotation axis; and a        holding portion that holds a work piece for forming the worm        screw and is rotatable. The cutter member is inclined with        respect to an axial center of the work piece at a predetermined        angle (mount angle). When a lead angle of the worm screw is        different from the mount angle, the mount angle is calculated by        formulae (1), (2), (3), (4) and (5) below.

mount angle=tan⁻¹ {n×pitch/(n×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

-   -   in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4)

-   -   in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5)

where D1≠0, ΔT≠0, and n indicates a number of threads.

The present invention is an invention of manufacturing a worm screw. Thesame effect as in the first aspect can be achieved.

Particularly, the screw manufacturing method of the present inventionhas effect such that it becomes difficult for the inserts to interferewith the worm screw, as shown in TABLES 4 and 5 for later-explainedfourth and fifth embodiments, upon rotating the work piece and thecutter member, for example, in order to manufacture the worm screw ofwhich lead angle is designed to satisfy the formula (X) above.

Specifically, in a worm screw having a large difference between a valleydiameter and an outer diameter and having a special shape of the screwthread (cross-sectional shape is orthogonal to a direction of a seriesof threads), use of the screw manufacturing method of the presentinvention can shorten machining time while maintaining machiningaccuracy.

-   -   Further, a third aspect of the present invention provides a        screw manufacturing method for manufacturing a metric screw        thread. The method uses: an annular cutter member that has a        plurality of inserts radially arranged and is rotatable on its        rotation axis, and a holding portion that holds a work piece for        forming the metric screw thread and is rotatable. The cutter        member is inclined with respect to an axial center of the work        piece at a predetermined angle (mount angle). When a lead angle        of the metric screw thread is different from the mount angle,        the mount angle is calculated by formulae (1), (2) and (3)        below.

mount angle=tan⁻¹ {n×pitch/(n×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

where D1≠0, ΔT≠0, and n indicates a number of threads.

The present invention is an invention of manufacturing a metric screwthread. The same effect as in the first aspect can be achieved.

Particularly, the screw manufacturing method of the present inventionhas effect such that it becomes difficult for the inserts to interferewith the metric screw thread, as shown in TABLES 7 to 12 forlater-explained sixth to eleventh embodiments, upon rotating the workpiece and the cutter member, for example, in order to manufacture themetric screw thread of which lead angle is designed to satisfy theformula (X) above.

Also, as is clear from the later-explained embodiments, if the leadangle in a design drawing of the metric screw thread falls below 7°, theinterference is not necessarily heavy upon going in and going out evenif the fluctuation is 0%. Depending on a level of inspection, themanufactured screw may be accepted. However, if the lead angle exceeds7°, the interference becomes heavy upon going in and going out when thefluctuation is 0%. Thus, it is preferable to set the mount angle toconform to the above formulae (1), (2) and (3).

-   -   In a fourth aspect of the present invention, the ΔT may be set        as in formulae (6) and (7) below.

in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.6≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}  (6)

in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}×0.6  (7)

By setting as above, as is clear from later-described TABLES 1 to 12,the interference upon both going in and out between the curved line ofthe screw and the moving paths of the inserts can be further reduced.

-   -   In a fifth aspect of the present invention, D1 can be set to be        the outer diameter of the screw or the valley diameter of the        screw.

By setting as above, as is clear from the later-described TABLES 1 to12, the interference upon going in or going out between the curved lineof the screw and the moving paths of the inserts can be null.

-   -   A sixth aspect of the present invention provides an annular        whirling cutter that has a plurality of inserts radially        arranged and is rotatable on its rotation axis. The whirling        cutter is inclined with respect to an axial center of a work        piece for manufacturing a medical screw at a predetermined angle        (mount angle). In case that a lead angle of the medical screw is        different from the mount angle, formulae (1), (2), (3), (4)        and (5) below are satisfied.

mount angle=tan⁻¹ {n×pitch/(n×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4)

in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5)

where D1≠0, ΔT≠0, and n indicates a number of threads.

Even if a lead angle of the medical screw, for example, is designed tosatisfy the formula (X) above or the medical screw has a special shapespecific to medical screws, as in the first aspect, when the medicalscrew is manufactured using the whirling cutter of the presentinvention, it becomes difficult for the inserts to interfere with themedical screw upon rotating the work piece and the whirling cutter.

Particularly, if the mount angle is set smaller (shallower) than thelead angle (i.e., 0<ΔT), it becomes difficult to hit especially a sideface of a tip end of the screw thread. Conversely, if the mount angle isset larger (deeper) than the lead angle (i.e., 0>ΔT), it becomesdifficult to hit especially to a side face of a base end of the screwthread.

Accordingly, when a medical screw is manufactured using the whirlingcutter of the present invention, moving paths of the inserts areinhibited from interfering with a desired curved line of the screw uponboth going in and out. Thereby, the screw provided with a targetedcurved line can be manufactured in a preferred manner.

Also in the present invention, as compared to thread rolling, a widevariety of products in small quantities can be easily manufactured.Moreover, as compared to turning, machining time can be shortened. Also,continuous machining can be applied to one piece of work piece. Thus, ajoining process is not necessary. Machining accuracy is advantageouslyhigh.

-   -   A seventh aspect of the present invention provides an annular        whirling cutter that has a plurality of inserts radially        arranged and is rotatable on its rotation axis. The whirling        cutter is inclined with respect to an axial center of a work        piece for manufacturing a worm screw at a predetermined angle        (mount angle). In case that a lead angle of the worm screw is        different from the mount angle, formulae (1), (2), (3), (4)        and (5) below are satisfied.

mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4)

in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5)

where D1≠0, ΔT≠0, and n indicates a number of threads.

The present invention is an invention of a whirling cutter thatmanufactures a worm screw. The same effect as in the sixth aspect can beachieved.

Particularly, use of the whirling cutter of the present invention haseffect such that it becomes difficult for the inserts to interfere withthe worm screw, upon rotating the work piece and the whirling cutter, incase that a lead angle of the worm screw, for example, is designed tosatisfy the formula (X) above.

-   -   An eighth aspect of the present invention provides an annular        whirling cutter that has a plurality of inserts radially        arranged and is rotatable on its rotation axis, wherein the        whirling cutter is inclined with respect to an axial center of a        work piece for manufacturing a metric screw thread at a        predetermined angle (mount angle), and, in case that a lead        angle of the metric screw thread is different from the mount        angle, formulae (1), (2) and (3) below are satisfied.

mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

where D1≠0, ΔT≠0, and n indicates a number of threads.

The present invention is an invention of a whirling cutter thatmanufactures a metric screw thread. The same effect as in the sixthaspect can be achieved.

Particularly, use of the whirling cutter of the present invention haseffect such that it becomes difficult for the inserts to interfere withthe metric screw thread, upon rotating the work piece and the whirlingcutter, in case that a lead angle of the metric screw thread, forexample, is designed to satisfy the formula (X) above.

-   -   A ninth aspect of the present invention provides a screw        manufacturing machine including: an annular whirling cutter that        has a plurality of inserts radially arranged and is rotatable on        its rotation axis; and a main spindle that coaxially holds a        base of a work piece for manufacturing a medical screw and        rotates the work piece. The whirling cutter is inclined with        respect to an axial center of the work piece at a predetermined        angle (mount angle). When a lead angle of the medical screw is        different from the mount angle, the mount angle satisfies        following formulae (1), (2), (3), (4) and (5).

mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4)

in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5)

where D1≠0, ΔT≠0, and n indicates a number of threads.

When a medical screw is manufactured using the screw manufacturingmachine of the present invention, in the same manner as in the firstaspect, for example, even if the lead angle of the medical screw isdesigned to satisfy a formula (X) above or the medical screw has aspecial shape specific to medical screws, it becomes difficult forinserts to interfere with the medical screw upon rotating the work pieceand the whirling cutter.

Particularly, if the mount angle is made smaller (shallower) than thelead angle (i.e., 0<ΔT), it becomes difficult to hit especially a sideface of a tip end of the screw thread. Conversely, if the mount angle ismade larger (deeper) than the lead angle (i.e., 0>ΔT), it becomesdifficult to hit especially to a side face of a base end of the screwthread.

Accordingly, when a medical screw is manufactured using the screwmanufacturing machine of the present invention, moving paths of theinserts are inhibited from interfering with a desired curved line of thescrew upon both going in and out. Thereby, the screw provided with atargeted curved line can be manufactured in a preferred manner.

Also in the present invention, as compared to thread rolling, a widevariety of products in small quantities can be easily manufactured.Moreover, as compared to turning, machining time can be shortened. Also,continuous machining can be applied to one piece of work piece. Thus, ajoining process is not necessary. Machining accuracy is advantageouslyhigh.

-   -   A tenth aspect of the present invention provides a screw        manufacturing machine including: an annular whirling cutter that        has a plurality of inserts radially arranged and is rotatable on        its rotation axis; and a main spindle that coaxially holds a        base of a work piece for manufacturing a worm screw and rotates        the work piece. The whirling cutter is inclined with respect to        an axial center of the work piece at a predetermined angle        (mount angle). When a lead angle of the worm screw is different        from the mount angle, the mount angle satisfies following        formulae (1), (2), (3), (4) and (5).

mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4)

in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5)

where D1≠0, ΔT≠0, and n indicates a number of threads.

The present invention is an invention of a screw manufacturing machinethat manufactures a worm screw. The same effect as in the ninth aspectcan be achieved.

Particularly, use of the screw manufacturing machine of the presentinvention has effect such that it becomes difficult for the inserts tointerfere with the worm screw, upon rotating the work piece and thewhirling cutter, in case that a lead angle of the worm screw, forexample, is designed to satisfy the formula (X) above.

-   -   Further, an eleventh aspect of the present invention provides a        screw manufacturing machine including: an annular whirling        cutter that has a plurality of inserts radially arranged and is        rotatable on its rotation axis; and a main spindle that        coaxially holds a base of a work piece for manufacturing a        metric screw thread and rotates the work piece. The whirling        cutter is inclined with respect to an axial center of the work        piece at a predetermined angle (mount angle). When a lead angle        of the metric screw thread is different from the mount angle,        the mount angle satisfies following formulae (1), (2) and (3).

mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

where D1≠0, ΔT≠0, and n indicates a number of threads.

The present invention is an invention of a screw manufacturing machinethat manufactures a metric screw thread. The same effect as in the ninthaspect can be achieved.

Particularly, use of the screw manufacturing machine of the presentinvention has effect such that it becomes difficult for the inserts tointerfere with the metric screw thread, upon rotating the work piece andthe whirling cutter, in case that a lead angle of the metric screwthread, for example, is designed to satisfy the formula (X) above.

Here, screws subject to the present invention include ordinarymechanical screws and medical screws. The present invention is amanufacturing method which is preferred to manufacture screws especiallyhaving special shapes such as medical screws.

Examples of the ordinary mechanical screws include various screwsdefined in JIS, e.g., metric screw threads, worm screws, unifiedthreads, trapezoidal threads, buttress threads, and others.

The medical screws mean screws (implants) used inside bodies of humansand animals.

Examples of cases where the interference between the screw and theinserts becomes large in a medical screw include cases where: its pitchis larger than that of an ordinary mechanical screw (e.g., equal to orlarger than 2.0 mm); a number of thread is larger than that of asingle-threaded screw, e.g., double-threaded screw; a screw is deepthreaded (a difference between an outer diameter and a valley diameteris large, e.g., equal to or larger than 2.0 mm); and a lead angle of atarget screw is large (e.g., equal to or larger than 15°).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view illustrating a manufacturing method of amedical screw by a thread whirling method.

FIG. 2 is an explanatory view illustrating a whirling cutter providedwith inserts.

FIG. 3A is a front view of the screw, and FIG. 3B is an explanatory viewshowing part of the screw being enlarged and fractured.

FIG. 4 is a perspective view of the insert used in a first embodiment.

FIG. 5A is an explanatory view illustrating a state of interference incase that a fluctuation is set to −100% in the first embodiment, FIG. 5Bis an explanatory view illustrating a state of interference in case thatthe fluctuation is set to −80%, FIG. 5C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto −60%, and FIG. 5D is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to −40%.

FIG. 6A is an explanatory view illustrating a state of interference incase that the fluctuation is set to −20% in the first embodiment, FIG.6B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to 0%, FIG. 6C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +20%, and FIG. 6D is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +40%.

FIG. 7A is an explanatory view illustrating a state of interference incase that the fluctuation is set to +60% in the first embodiment, FIG.7B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to +80%, and FIG. 7C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +100%.

FIG. 8 is a perspective view showing an insert used in a secondembodiment.

FIG. 9A is an explanatory view illustrating a state of interference incase that a fluctuation is set to −100% in the second embodiment, FIG.9B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to −80%, FIG. 9C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto −60%, and FIG. 9D is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to −40%.

FIG. 10A is an explanatory view illustrating a state of interference incase that the fluctuation is set to −20% in the second embodiment, FIG.10B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to 0%, FIG. 10C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +20%, and FIG. 10D is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +40%.

FIG. 11A is an explanatory view illustrating a state of interference incase that the fluctuation is set to +60% in the second embodiment, FIG.11B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to +80%, and FIG. 11C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +100%.

FIG. 12 is a cross-sectional view showing a cross section along a centeraxis of a medical screw according to a third embodiment.

FIG. 13A is an explanatory view illustrating a state of interference incase that a fluctuation is set to +100% in the third embodiment, FIG.13B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to +60%, FIG. 13C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +40%, and FIG. 13D is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +0%.

FIG. 14A is an explanatory view showing a worm screw according to afourth embodiment, and FIG. 14B is a cross-sectional view showing across section along a center axis of the worm screw.

FIG. 15A is an explanatory view illustrating a state of interference incase that a fluctuation is set to +100% in the fourth embodiment, FIG.15B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to +60%, FIG. 15C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +40%, and FIG. 15D is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +0%.

FIG. 16 is a cross-sectional view showing a cross section along a centeraxis of a worm screw according to a fifth embodiment.

FIG. 17A is an explanatory view illustrating a state of interference incase that a fluctuation is set to +100% in the fifth embodiment, FIG.17B is an explanatory view illustrating a state of interference in casethat the fluctuation is set to +60%, FIG. 17C is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +40%, and FIG. 17D is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +0%.

FIG. 18 is a cross-sectional view showing a cross section along a centeraxis of a metric screw thread according to a sixth embodiment.

FIG. 19A is an explanatory view illustrating a state of interference incase that a fluctuation is set to +100% in the sixth embodiment (pitch:0.8), FIG. 19B is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +0%, FIG. 19C is anexplanatory view illustrating a state of interference in case that afluctuation is set to +100% in a seventh embodiment (pitch: 1.0), andFIG. 19D is an explanatory view illustrating a state of interference incase that the fluctuation is set to +0%.

FIG. 20A is an explanatory view illustrating a state of interference incase that a fluctuation is set to +100% in an eighth embodiment (pitch:1.25), FIG. 20B is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +0%, FIG. 20C is anexplanatory view illustrating a state of interference in case that afluctuation is set to +100% in a ninth embodiment (pitch: 1.5), and FIG.20D is an explanatory view illustrating a state of interference in casethat the fluctuation is set to +0%.

FIG. 21A is an explanatory view illustrating a state of interference incase that a fluctuation is set to +100% in a tenth embodiment (pitch:1.75), and FIG. 21B is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +0%.

FIG. 22A is an explanatory view illustrating a state of interference incase that a fluctuation is set to +100% in an eleventh embodiment(pitch: 2.0), FIG. 22B is an explanatory view illustrating a state ofinterference in case that the fluctuation is set to +60%, FIG. 22C is anexplanatory view illustrating a state of interference in case that thefluctuation is set to +40%, and FIG. 22D is an explanatory viewillustrating a state of interference in case that the fluctuation is setto +0%.

FIG. 23 is an explanatory view illustrating a problem in prior art.

EXPLANATION OF REFERENCE NUMERALS

-   -   1, 31, 35, 41, 51, 53, 61 . . . screw    -   3 . . . work piece    -   5 . . . screw portion    -   7 . . . main spindle    -   9 . . . whirling cutter    -   10 . . . screw manufacturing machine    -   11 . . . cutter head    -   13, 21 . . . insert    -   17 . . . through hole

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be describedtogether with the accompanying drawings.

First Embodiment

a) First, an outline will be provided on a manufacturing method of amedical screw by a thread whirling method.

As shown in FIG. 1, the thread whirling method according to the presentembodiment uses a main spindle 7 and a whirling cutter 9 to form a screwportion 5 on a surface of a rod material (work piece) 3 which is to be amedical screw (hereinafter, simply referred to as a screw) 1. The mainspindle 7 coaxially holds a base of the work piece 3 and rotates thework piece 3. The whirling cutter 9 is arranged to incline at a mountangle β (°) with respect to an axial direction of the work piece 3 androtates.

The whirling cutter 9 is an annular device which is rotated by a notshown tool spindle. As shown in FIG. 2, a plurality of, e.g., nine,inserts 13 are radially arranged on an annular cutter head 11 of thewhirling cutter 9.

Each of the inserts 13 is secured to the cutter head 11 by a fixationscrew 15. A machine that includes the main spindle 7 and the whirlingcutter 9 and manufactures the screw 1 by the thread whirling method isreferred to as a screw manufacturing machine 10.

For example, when the screw 1, as shown in FIGS. 3A and 3B, is to beprepared by thread whirling machining, the following steps are taken.

First, as shown in FIG. 1, the rod-like work piece 3 is inserted to arotation center of the main spindle 7.

Next, the work piece 3 is inserted to a through hole 17 in a center ofthe whirling cutter 9. Also, the whirling cutter 9 is inclined at apredetermine angle (mount angle β) with respect to a center axis of thework piece 3. In this state, the work piece 3 is forwarded at apredetermined speed to its axial direction (upward direction in FIG. 1)while being rotated to a predetermined direction (direction A in FIGS. 1and 2). At the same time, the whirling cutter 9 is rotated to the samedirection at a rotation speed higher than a rotation speed of the workpiece 3, thereby to prepare a screw by the plurality of inserts 13.

In detail, as shown in FIG. 2, a rotation center of the whirling cutter9 and an axial center of the work piece 3 are arranged such that thework piece 3 is in contact with the insert 13 (the axial center of thework piece 3 is arranged in an upward direction in the same figure).When the whirling cutter 9 rotates, the screw portion 5 is formed by therespective inserts 13 which sequentially come into contact with the workpiece 3.

The medical screw 1 to be manufactured in the present embodiment is asingle-threaded screw. Here, in order to prepare a single-threadedscrew, the insert 13 having one-ridged cutting portion 19 as shown inFIG. 4 is used. A shape of the insert 13 is parallelogram. However,shapes such as a diamond and a triangle, for example, can be alsohandled. Further details of the shape will be determined according to ashape of a screw to be prepared.

b) Next, how to set the mount angle β will be described.

The mount angle β is determined by a shape of the screw 1 to beprepared.

Thus, first of all, as shown in FIGS. 3A and 3B, numerical values whichspecify the shape of the screw 1 are read from a drawing of the screw 1(here, a single-threaded screw) to be prepared.

For example, typical data which specify the shape of the screw 1 is asbelow. Other than below, there are data for specifying athree-dimensional surface shape (curve) of the screw portion 5. Here,the numerical data of the screw 1 to be prepared by the inserts 13 areshown.

Whole screw length in axial direction: 50.0 mm

Screw portion length in axial direction: 30.0 mm

Screw outer diameter: φ6.0 mm

Screw valley diameter: φ4.0 mm

Pitch: 5.0 mm

Thread lead angle: 17.66°

The mount angle β is different from the lead angle of the screw 1. Thatis, D1 in the above formula (1) is different from a pitch diameter ofthe above formula (X).

c) Next, an example of the method of manufacturing the screw 1 usingthread whirling machining will be described.

Here, a case of preparing the screw 1 having the aforementionedmeasurements will be described.

As shown in FIG. 1, the work piece 3 is attached and secured to therotation center of the main spindle 7, and inserted to the through hole17 in the center of the whirling cutter 9. Also, the whirling cutter 9is inclined at the mount angle β with respect to the center axis of thework piece 3.

The mount angle β is calculated using formulae (1), (2), (3), (4) and(5) below. Here, the mount angle β is an angle at which the whirlingcutter 9 is inclined with respect to the center axis of the work piece 3upon thread whirling machining.

mount angle=tan⁻ {n×pitch/(π×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4)

in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5)

where D1 (mm)≠0, ΔT (mm)≠0, and n indicates a number of threads.

As for the work piece 3, a cylindrical rod made of titanium alloy wasused which has a length of 2.5 m×an outer diameter of 0.0 mm.

Then, according to machining conditions below, the screw 1 having atarget shape shown in FIGS. 3A and 3B is to be prepared.

Main spindle rotation speed: 10 rpm

Work piece forward speed: 2.75 mm/rev

Tool spindle rotation speed: 2000 rpm

As shown in TABLE 1 below, the screw 1 was prepared by changing D1 tochange the mount angle β. At that time, presence/absence of interference(interference between a curved line of the screw 1 and moving paths ofthe inserts 13) was studied. In detail, a simulation was conducted by aknown CAD. Also, the screw 1 was actually prepared to check a state ofinterference.

As for the CAD, a three-dimensional CAD USG NX4 was used.

The result is shown in the TABLE 1 and FIGS. 5A to 5D, 6A to 6D and 7Ato 7C.

TABLE 1 Lead L 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 4.00 4.20 4.40 4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00Fluctuation range = ΔT −1.00 −0.80 −0.60 −0.40 −0.20 0.00 +0.20 +0.40+0.60 +0.80 +1.00 Mount angle 21.70 20.75 19.89 19.09 18.34 17.66 17.0216.42 15.87 15.34 14.86 Determination ⊚ ◯ ◯ Δ X X X Δ ◯ ◯ ⊚

In the above TABLE 1, “Fluctuation” indicates a proportion offluctuation (in case that a maximum fluctuation range of 1.00 is set tobe 100%) in D1 from an intermediate value (D1=5.00: ΔT=0). “Revisedfluctuation” indicates a value obtained by converting the fluctuation of200% to 100%. “Fluctuation range” indicates a range of actualfluctuation (corresponding to the above ΔT) from D1=5.00.

In the result of Determination, “⊚” indicates that “interference uponeither going in or out is completely avoided so that a targetedscrew-thread shape can be substantially obtained”. “◯” indicates that“interference upon either going in or out is not completely avoided, butmachining to an extent not to be called a shape defect can be performed.“A” indicates that “interference upon either going in or out isfrequent, but products can be accepted depending on the inspectionlevel”. “X” indicates that “interference upon both going in and out isfrequent, and only the products determined to have a shape defect can beproduced”.

Here, the “targeted screw-thread shape” is not only an idealscrew-thread shape which follows a screw curved line, but also ascrew-thread shape in which interference can be caused only in either ofportions on a screw outer diameter side or on a screw base end side(valley side).

Further, in FIGS. 5A to 5D, 6A to 6D and 7A to 7C, a white portion inthe center indicates the shape of the work piece 3 before machining.Gray portions on the right and left sides indicate the shape aftermachining. Gray portions (inside an elliptic circle) in the centralwhite portion of the work piece 3 indicate portions where interferenceoccurs. The elliptic circle is omitted in FIG. 6D and the figures havinga larger number than 6D.

As is clear from TABLE 1 and FIGS. 5A to 5D, 6A to 6D and 7A to 7C, ashape that evades the curved line of the screw 1 is achieved by changingD1 to adjust the mount angle β, more particularly, by increasing thefluctuation of D1 to increase the difference between the mount angle βand the lead angle (i.e., by increasing the fluctuation). It isunderstood that the interference upon either going in or out can bereduced.

Particularly, for example, as shown in FIGS. 5A to 5D and 6A to 6B, ifthe fluctuation is increased, the shape of the interfered portions ischanged from two fan-shaped sectors (see FIG. 6B, for example) expandingupward and downward to a fan-shaped sector (see FIG. 5A, for example)expanding in one of the directions (upward, for example).

Accordingly, it is understood that the screw 1 having a smallerinterference (or no interference) either upon going in or out can beobtained.

Moreover, as is clear from comparison between FIGS. 5A to 5D and FIG.6A, it is understood that, as the minus (−) fluctuation is larger than−20% fluctuation, interference on the screw base end side (valley side)can be reduced (triangular gray portion has become small). Similarly, incomparison between FIGS. 6D and 7A to 7C and FIG. 6C, it is understoodthat, as the plus (+) fluctuation is larger than +20% fluctuation,interference on the portion on the screw outer diameter side can bereduced (triangular gray portion becomes small).

Also, as is clear from FIG. 6B (0% fluctuation), if D1 is (screw valleydiameter+screw outer diameter)/2 (i.e., ΔT=0), interference occurs toboth the portions on the screw outer diameter side and the screw baseend side (valley side). Thus, use of the manufactured screw becomes aproblem. That is, if interference occurs to both the portions on thescrew outer diameter side and the screw base end side (valley side), itbecomes difficult to fasten the screw with good accuracy. Furthermore,the interference may cause backlash of the screw.

e) As noted above, in the present embodiment, by setting values of themount angle β to be different from the lead angle, the screw 1 in theshape which reduces interference between the moving paths of the inserts13 and the curved line of the screw 1 upon going in or out can beobtained in a preferred manner. Further, since interference does notnecessarily occur to both the portions of the screw outer diameter sideand the screw base end side (valley side), there is no problem in use ofthe manufactured screw 1.

That is, in the present embodiment, since interference can be avoidedfrom occurring to both the portions on the screw outer diameter side andthe screw base end side (valley side), the screw 1 can be rotatedwithout problem when fastening, etc. is performed using the manufacturedscrew 1.

In detail, as is clear from the above TABLE 1, interference between thecurved line of the screw 1 and the moving paths of the inserts 13 upongoing in or out can be all the more reduced by setting as below.

in case ΔT>0,

{(screw outer diameter−screw valley diameter)/2}×0.6≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}

in case ΔT<0,

−{(screw outer diameter−screw valley diameter)/2}ΔT≦−{(screw outerdiameter−screw valley diameter)/2}×0.6

The above “(screw outer diameter−screw valley diameter)” indicates themaximum fluctuation range. For example, if the fluctuation is +60%(revised fluctuation=+30%), ΔT={(screw outer diameter−screw valleydiameter)×0.3}.

Specifically, by setting D1 upon calculating the mount angle β to thescrew outer diameter (+100% fluctuation) or the screw valley diameter(−100% fluctuation), no interference between the moving paths of theinserts 13 and the curved line of the screw 1 occurs upon either goingin or out.

Also, even the screw 1 having a special shape such as a medical screwcan be advantageously prepared by a single process, and not by processesincluding a plurality of passes.

Second Embodiment

Now, a second embodiment will be described. Descriptions of the samecontents as those in the above first embodiment will not be repeated.

A medical screw to be manufactured in the present embodiment is adouble-threaded screw. As shown in FIG. 8, an insert 21 to be used in athread whirling method by which the medical screw is to be manufacturedincludes a two-ridged cutting portion 23, 25.

In the present embodiment, an example of typical data which specify theshape of the screw is as below.

Whole screw length in axial direction: 50.0 mm

Screw portion length in axial direction: 30.0 mm

Screw outer diameter: φ4.0 mm

Screw valley diameter: φ2.4 mm

Pitch: 3.42 mm

Thread lead angle: 18.79°

The mount angle β is calculated using the formulae (1), (2), (3), (4)and (5) in the above first embodiment.

As shown in TABLE 2 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 2 and FIGS. 9A to 9D, 10Ato 10D and 11A to 11C.

TABLE 2 Lead L 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42 3.42Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 2.40 2.56 2.72 2.88 3.04 3.20 3.36 3.52 3.68 3.38 4.00Fluctuation range = ΔT −0.80 −0.64 −0.48 −0.32 −0.16 0.00 +0.16 +0.32+0.48 +0.64 +0.80 Mount angle 24.40 23.04 21.81 20.71 19.70 18.79 17.9517.19 16.48 15.83 15.22 Determination ⊚ ◯ ◯ Δ X X X Δ ◯ ◯ ⊚

Meanings of words in TABLE 2 and meanings of colors (thickness) in FIGS.9A to 9D, 10A to 10D and 11A to 11C are the same as those in the abovefirst embodiment.

As is clear from TABLE 2 and FIGS. 9A to 9D, 10A to 10D and 11A to 11C,it is understood that the interference upon going in and out can bereduced by changing D1 to adjust the mount angle β in the same manner asin the first embodiment.

Accordingly, in the present embodiment, the same effect as in the firstembodiment is achieved.

Also in the insert 21 for the double-threaded screw, its cutting surfaceis larger in its width direction as compared to its height direction, inorder to form a double-threaded screw portion at once, than that theinsert for the single-threaded screw. Since interference is easy tooccur between the insert 21 and the screw portion, it is not easy toform a desired screw thread. However, the manufacturing method accordingto the present embodiment allows easy preparation of a screw having adesired shape.

Further, a double-threaded screw can be advantageously prepared by asingle process, and not by processes including a plurality of passes.

Third Embodiment

Now, a third embodiment will be described. Descriptions of the samecontents as those in the above second embodiment will not be repeated.

A screw to be manufactured in the present embodiment is adouble-threaded medical screw 31, as shown in FIG. 12. Although notshown, inserts used in a thread whirling method by which the medicalscrew 31 is manufactured include a two-ridged cutting portion. Unit oflength in FIG. 12 is mm.

In the present embodiment, an example of typical data which specify theshape of the screw is as below.

Whole screw length in axial direction: 30 mm

Screw portion length in axial direction: 20 mm

Screw outer diameter: φ5.5 mm

Screw valley diameter: φ4.0 mm

Intermediate value of screw: φ4.75 mm

Pitch: 5.35 mm

Thread lead angle: 19.72°

The mount angle β is calculated using the formulae (1), (2), (3), (4)and (5) in the above first embodiment.

As shown in TABLE 3 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 3 and FIGS. 13A to 13D.

TABLE 3 Lead L 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35 5.35Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 4.00 4.15 4.30 4.45 4.60 4.75 4.90 5.05 5.20 5.35 5.50Fluctuation range = ΔT −0.75 −0.60 −0.45 −0.30 −0.15 0.00 +0.15 +0.30+0.45 +0.60 +0.75 Mount angle 23.06 22.31 21.61 20.94 20.31 19.72 19.1618.64 18.13 17.66 17.20 Determination ⊚ ◯ ◯ Δ X X X Δ ◯ ◯ ⊚

Meanings of words in TABLE 3 and meanings of colors (thickness) in FIGS.13A to 13D are the same as those in the above first embodiment.

As is clear from TABLE 13 and FIGS. 13A to 13D, it is understood thatthe interference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the second embodiment.

Accordingly, in the present embodiment, the same effect as in the secondembodiment is achieved. In this way, the effect of the present inventioncan be achieved regardless of designs such as an outer diameter/valleydiameter of a screw.

Fourth Embodiment

Now, a fourth embodiment will be described. Descriptions of the samecontents as those in the above first embodiment will not be repeated.

A screw to be manufactured in the present embodiment is adouble-threaded worm screw (JIS B1723/3) 35, as shown in FIGS. 14A and14B. Although not shown, inserts used in a thread whirling method bywhich the worm screw 35 is manufactured include a two-ridge cuttingportion.

In the present embodiment, an example of typical data which specify theshape of the screw is as below. Unit of length in FIG. 14B is mm.

Whole screw length in axial direction: 11 mm

Screw portion length in axial direction: 10 mm

Screw outer diameter: φ6 mm

Intermediate value of screw: φ5.125 mm

Screw valley diameter: φ4.25 mm

Pitch: 2.872 mm

Thread lead angle: 10.1141°

The mount angle β is calculated using the formulae (1), (2), (3), (4)and (5) in the above first embodiment.

As shown in TABLE 4 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 4 and FIGS. 15A to 15D.

TABLE 4 Lead L 2.872 2.872 2.872 2.872 2.872 2.872 2.872 2.872 2.8722.872 2.872 Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80%+100% Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30%+40%  +50% D1 4.250 4.425 4.600 4.775 4.950 5.125 5.300 5.475 5.6505.825 6.000 Fluctuation range = ΔT −0.875 −0.7 −0.525 −0.35 −0.175 0.00+0.175 +0.35 +0.525 +0.7 +0.875 Mount angle 12.14 11.67 11.24 10.8410.46 10.11 9.79 9.48 9.19 8.92 8.66 Determination ⊚ ◯ ◯ Δ X X X Δ ◯ ◯ ⊚

Meanings of words in TABLE 4 and meanings of colors (thickness) in FIGS.15A to 15D are the same as those in the above first embodiment.

As is clear from TABLE 4 and FIGS. 15A to 15D, it is understood that theinterference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the first embodiment.

Accordingly, in the present embodiment, the same effect as in the firstembodiment is achieved even with the ordinary double-threaded worm screw35.

Fifth Embodiment

Now, a fifth embodiment will be described. Descriptions of the samecontents as those in the above first embodiment will not be repeated.

A screw to be manufactured in the present embodiment is atriple-threaded worm screw (JIS B1723/3) 41, as shown in FIG. 16.Although not shown, inserts used in a thread whirling method by whichthe worm screw 41 is manufactured include a three-ridged cuttingportion.

In the present embodiment, an example of typical data which specify theshape of the screw is as below. Unit of length in FIG. 16 is mm.

Whole screw length in axial direction: 12 mm

Screw portion length in axial direction: 12 mm

Screw outer diameter: φ7 mm

Intermediate value of screw: 6.000 mm

Screw valley diameter: φ5.000 mm

Pitch: 4.867 mm

Thread lead angle: 14° 28′ 39″

The mount angle β is calculated using the formulae (1), (2), (3), (4)and (5) in the above first embodiment.

As shown in TABLE 5 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 5 and FIGS. 17A to 17D.

TABLE 5 Lead L 4.867 4.867 4.867 4.867 4.867 4.867 4.867 4.867 4.8674.867 4.867 Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80%+100% Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30%+40%  +50% D1 5.000 5.200 5.400 5.600 5.800 6.000 6.200 6.400 6.6006.800 7.000 Fluctuation range = ΔT −1.0 −0.8 −0.6 −0.4 −0.2 0.00 +0.2+0.4 +0.6 +0.8 +1.0 Mount angle 17.22 16.59 16.01 15.46 14.95 14.4814.03 13.61 13.21 12.83 12.48 Determination ⊚ ◯ ◯ Δ X X X Δ ◯ ◯ ⊚

Meanings of words in TABLE 5 and meanings of colors (thickness) in FIGS.17A to 17D are the same as those in the above first embodiment.

As is clear from TABLE 5 and FIGS. 17A to 17D, it is understood that theinterference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the first embodiment.

Accordingly, in the present embodiment, the same effect as in the firstembodiment is achieved even with the ordinary triple-threaded worm screw41.

Sixth Embodiment

Now, a sixth embodiment will be described. Descriptions of the samecontents as those in the above first embodiment will not be repeated.

Screws to be manufactured in the present embodiment are ordinarysingle-threaded metric screw threads 51 and 53, as shown in FIG. 18.

The screw 51 is an external screw and the screw 53 is an internal screw.In these metric screw threads 51 and 53, a relation among its pitch (p),fundamental triangle height (H), and others in case that an outerdiameter of the screws is φ5 mm, for example, is defined as shown inTABLE 6 below.

TABLE 6 Valley diameter of Pitch H H/8 (5/8)H P/4 screw 0.80 0.6928200.086603 0.433013 0.2000 4.133975 1.00 0.866025 0.108253 0.541266 0.25003.917469 1.25 1.082532 0.135317 0.676583 0.3125 3.646835 1.50 1.2990380.162380 0.811899 0.3750 3.376203 1.75 1.515544 0.189443 0.947215 0.43753.105570 2.00 1.732051 0.216506 1.082532 0.5000 2.834936

Although not shown, inserts used in a thread whirling method by whichthe metric screw threads 51 and 53 are manufactured include a one-ridgedcutting portion.

In the present embodiment, an example of typical data which specify theshape of the screw (e.g., the metric screw thread 51 as an externalscrew) is as below.

Whole screw length in axial direction: 15 mm

Screw portion length in axial direction: 10 mm

Screw outer diameter: φ5 mm

Intermediate value of screw: φ4.567 mm

Screw valley diameter: φ4.134 mm

Pitch: 0.8 mm

Thread lead angle: 3.19°

The mount angle β is calculated using formulae (1), (2) and (3) below.

mount angle=tan⁻¹ {n×pitch/(n×D1)}  (1)

D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)

screw valley diameter≦D1≦screw outer diameter  (3)

As shown in TABLE 7 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 7 and FIGS. 19A and 19B.

TABLE 7 Lead L 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 4.134 4.221 4.307 4.394 4.480 4.567 4.654 4.740 4.827 4.9135.000 Fluctuation range = ΔT −0.433 −0.346 −0.26 −0.173 −0.087 0.00+0.087 +0.173 +0.26 +0.346 +0.433 Mount angle 3.52 3.45 3.38 3.32 3.253.19 3.13 3.08 3.02 2.97 2.92 Determination ⊚ ◯ ◯ Δ Δ Δ Δ Δ ◯ ◯ ⊚

Meanings of words in TABLE 7 and meanings of colors (thickness) in FIGS.19A and 19B are the same as those in the above first embodiment.

As is clear from TABLE 7 and FIGS. 19A and 19B, it is understood thatthe interference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the first embodiment.

Accordingly, in the present embodiment, even in the ordinary metricscrew thread 51, the screw 51 which is shaped to reduce the interferencebetween the moving paths of the inserts and a curved line of the screw51 upon going in and out can be obtained in a preferred manner bysetting different values to the mount angle β and the lead angle.Further, since the interference is not caused on both portions on theouter side of the screw and the base end side (valley side) of thescrew, there is no problem in using the manufactured screw 51. To sumup, in the present embodiment, the interference can be inhibited fromoccurring to both the portions on the outer side of the screw and thebase end side (valley side) of the screw. Thus, upon fastening, etc.,using the manufactured screw 51, the screw 51 can be rotated withoutproblem.

Seventh Embodiment

Now, a seventh embodiment will be described. Descriptions of the samecontents as those in the above sixth embodiment will not be repeated.

A screw to be manufactured in the present embodiment is an ordinarysingle-threaded metric screw thread (external screw), as in the sixthembodiment, which is not shown. Especially, while its outer diameter isφ5 mm which is the same, its pitch is larger, i.e., 1.0 mm.

Although not shown, inserts used in a thread whirling method by whichthe metric screw thread is manufactured include a one-ridged cuttingportion.

In the present embodiment, an example of typical data which specify theshape of the metric screw thread is as below.

Whole screw length in axial direction: 15 mm

Screw portion length in axial direction: 10 mm

Screw outer diameter: φ5 mm

Intermediate value of screw: φ4.459 mm

Screw valley diameter: φ3.917 mm

Pitch: 1.0 mm

Thread lead angle: 4.08°

The mount angle β is calculated using the formulae (1), (2), and (3) inthe above sixth embodiment.

As shown in TABLE 8 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 8 and FIGS. 19C and 19D.

TABLE 8 Lead L 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 3.917 4.026 4.134 4.242 4.350 4.459 4.567 4.675 4.783 4.8925.000 Fluctuation range = ΔT −0.542 −0.433 −0.325 −0.217 −0.109 0.00+0.108 +0.216 +0.324 +0.433 +0.541 Mount angle 4.65 4.52 4.40 4.29 4.184.08 3.99 3.86 3.81 3.72 3.64 Determination ⊚ ◯ ◯ Δ Δ Δ Δ Δ ◯ ◯ ⊚

Meanings of words in TABLE 8 and meanings of colors (thickness) in FIGS.19C and 19D are the same as those in the above sixth embodiment.

As is clear from TABLE 8 and FIGS. 19C and 19D, it is understood thatthe interference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the sixth embodiment.

Accordingly, the present embodiment achieves the same effect as thesixth embodiment.

Eighth Embodiment

Now, an eighth embodiment will be described. Descriptions of the samecontents as those in the above sixth embodiment will not be repeated.

A screw to be manufactured in the present embodiment is an ordinarysingle-threaded metric screw thread (external screw), as in the sixthembodiment, which is not shown. Especially, while its outer diameter isφ5 mm which is the same, its pitch is larger, i.e., 1.25 mm.

Although not shown, inserts used in a thread whirling method by whichthe metric screw thread is manufactured include a one-ridged cuttingportion.

In the present embodiment, an example of typical data which specify theshape of the metric screw thread is as below.

Whole screw length in axial direction: 15 mm

Screw portion length in axial direction: 10 mm

Screw outer diameter: φ5 mm

Intermediate value of screw: φ4.323 mm

Screw valley diameter: φ3.647 mm

Pitch: 1.25 mm

Thread lead angle: 5.26°

The mount angle β is calculated using the formulae (1), (2), and (3) inthe above sixth embodiment.

As shown in TABLE 9 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 9 and FIGS. 20A and 20B.

TABLE 9 Lead L 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 3.647 3.782 3.917 4.053 4.188 4.323 4.459 4.594 4.729 4.8655.000 Fluctuation range = ΔT −0.676 −0.541 −0.406 −0.27 −0.135 0.00+0.136 +0.271 +0.406 +0.542 +0.677 Mount angle 6.23 6.01 5.80 5.61 5.435.26 5.10 4.95 4.81 4.68 4.55 Determination ⊚ ◯ ◯ Δ Δ Δ Δ Δ ◯ ◯ ⊚

Meanings of words in TABLE 9 and meanings of colors (thickness) in FIGS.20A and 20B are the same as those in the above sixth embodiment.

As is clear from TABLE 9 and FIGS. 20A and 20B, it is understood thatthe interference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the sixth embodiment.

Accordingly, the present embodiment achieves the same effect as thesixth embodiment.

Ninth Embodiment

Now, a ninth embodiment will be described. Descriptions of the samecontents as those in the above sixth embodiment will not be repeated.

A screw to be manufactured in the present embodiment is an ordinarysingle-threaded metric screw thread (external screw), as in the sixthembodiment, which is not shown. Especially, while its outer diameter isφ5 mm which is the same, its pitch is larger, i.e., 1.5 mm.

Although not shown, inserts used in a thread whirling method by whichthe metric screw thread is manufactured include a one-ridged cuttingportion.

In the present embodiment, an example of typical data which specify theshape of the metric screw thread is as below.

Whole screw length in axial direction: 15 mm

Screw portion length in axial direction: 10 mm

Screw outer diameter: φ5 mm

Intermediate value of screw: φ4.188 mm

Screw valley diameter: φ3.376 mm

Pitch: 1.5 mm

Thread lead angle: 6.5°

The mount angle β is calculated using the formulae (1), (2), and (3) inthe above sixth embodiment.

As shown in TABLE 10 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 10 and FIGS. 20C and 20D.

TABLE 10 Lead L 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 3.376 3.539 3.701 3.863 4.026 4.188 4.350 4.513 4.675 4.8385.000 Fluctuation range = ΔT −0.812 −0.678 −0.487 −0.325 −0.162 0.00+0.162 +0.325 +0.487 +0.65 +0.812 Mount angle 8.05 7.68 7.35 7.05 6.766.50 6.26 6.04 5.83 5.64 5.45 Determination ⊚ ◯ ◯ Δ Δ Δ Δ Δ ◯ ◯ ⊚

Meanings of words in TABLE 10 and meanings of colors (thickness) inFIGS. 20C and 20D are the same as those in the above first embodiment.

As is clear from TABLE 10 and FIGS. 20C and 20D, it is understood thatthe interference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the sixth embodiment.

Accordingly, the present embodiment achieves the same effect as thesixth embodiment.

Tenth Embodiment

Now, a tenth embodiment will be described. Descriptions of the samecontents as those in the above sixth embodiment will not be repeated.

A screw to be manufactured in the present embodiment is an ordinarysingle-threaded metric screw thread (external screw), as in the sixthembodiment, which is not shown. Especially, while its outer diameter isφ5 mm which is the same, its pitch is larger, i.e., 1.75 mm.

Although not shown, inserts used in a thread whirling method by whichthe metric screw thread is manufactured include a one-ridged cuttingportion.

In the present embodiment, an example of typical data which specify theshape of the metric screw thread is as below.

Whole screw length in axial direction: 15 mm

Screw portion length in axial direction: 10 mm

Screw outer diameter: φ5 mm

Intermediate value of screw: φ4.053 mm

Screw valley diameter: φ3.105 mm

Pitch: 1.75 mm

Thread lead angle: 7.83°

The mount angle β is calculated using the formulae (1), (2), and (3) inthe above sixth embodiment.

As shown in TABLE 11 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 11 and FIGS. 21A and 21B.

TABLE 11 Lead L 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 3.106 3.295 3.484 3.674 3.863 4.053 4.242 4.432 4.621 4.8115.000 Fluctuation range = ΔT −0.947 −0.758 −0.569 −0.379 −0.19 0.00+0.189 +0.379 +0.568 +0.758 +0.947 Mount angle 10.17 9.60 9.08 8.62 8.207.83 7.48 7.16 6.87 6.61 6.36 Determination ⊚ ◯ ◯ Δ Δ X Δ Δ ◯ ◯ ⊚

Meanings of words in TABLE 11 and meanings of colors (thickness) inFIGS. 21A and 21B are the same as those in the above first embodiment.

As is clear from TABLE 11 and FIGS. 21A and 21B, it is understood thatthe interference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the sixth embodiment.

Accordingly, the present embodiment achieves the same effect as thesixth embodiment.

Eleventh Embodiment

Now, an eleventh embodiment will be described. Descriptions of the samecontents as those in the above sixth embodiment will not be repeated.

A screw to be manufactured in the present embodiment is an ordinarysingle-threaded metric screw thread (external screw) as in the abovesixth embodiment, which is not shown. Especially, while its outerdiameter is φ5 mm which is the same, its pitch is larger, i.e., 2 mm.

Although not shown, inserts used in a thread whirling method by whichthe metric screw thread is manufactured include a one-ridged cuttingportion.

In the present embodiment, an example of typical data which specify theshape of the metric screw thread is as below.

Whole screw length in axial direction: 15 mm

Screw portion length in axial direction: 10 mm

Screw outer diameter: φ5 mm

Intermediate value of screw: φ3.917 mm

Screw valley diameter: 2.835 mm

Pitch: 2 mm

Thread lead angle: 9.23°

The mount angle β is calculated using the formulae (1), (2), and (3) inthe above first embodiment.

As shown in TABLE 12 below, the screw was prepared by changing D1 tochange the mount angle. At that time, presence/absence of interferencewas studied. The result is shown in the TABLE 12 and FIGS. 22A to 22D.

TABLE 12 Lead L 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00Fluctuation −100% −80% −60% −40% −20% 0 +20% +40% +60% +80% +100%Revised fluctuation  −50% −40% −30% −20% −10% 0 +10% +20% +30% +40% +50% D1 2.835 3.051 3.268 3.484 3.701 3.917 4.134 4.350 4.567 4.7835.000 Fluctuation range = ΔT −1.082 −0.866 −0.649 −0.433 −0.216 0.00+0.217 +0.433 +0.65 +0.866 +1.083 Mount angle 12.66 11.78 11.02 10.359.76 9.23 8.75 8.33 7.94 7.58 7.26 Determination ⊚ ◯ ◯ Δ Δ X Δ Δ ◯ ◯ ⊚

Meanings of terms in TABLE 12 and of colors (thickness) in FIGS. 22A to22D are the same as those in the first embodiment.

As is clear from TABLE 12 and FIGS. 22A to 22D, it is understood thatthe interference upon going in and out can be reduced by changing D1 toadjust the mount angle β in the same manner as in the sixth embodiment.

Thus, the present embodiment achieves the same effect as the sixthembodiment.

Accordingly, as is clear from the sixth to the eleventh embodiments, thesame effect as in the first embodiment is achieved in ordinary metricscrew threads.

The embodiments of the present invention have been described in theabove. However, the present invention should not be limited to the abovedescribed embodiments, and may be practiced in various forms within thetechnical scope of the present invention.

1-11. (canceled)
 12. A screw manufacturing method for manufacturing amedical screw, the method using: an annular cutter member that has aplurality of inserts radially arranged and is rotatable on its rotationaxis; and a holding portion that holds a work piece for forming themedical screw and is rotatable, the cutter member being inclined withrespect to an axial center of the work piece at a predetermined angle(mount angle), the method comprising a step of calculating the mountangle by formulae (1), (2), (3), (4) and (5) below, when a lead angle ofthe medical screw is different from the mount angle:mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) in case ΔT>0,{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5) where D1≠0, ΔT≠0, and nindicates a number of threads.
 13. The screw manufacturing methodaccording to claim 12, wherein the ΔT is set to be within ranges offormulae (6) and (7) below: in case ΔT>0,{(screw outer diameter−screw valley diameter)/2}×0.6≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}  (6) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}Δ≦T≦−{(screw outerdiameter−screw valley diameter)/2}×0.6  (7).
 14. The screw manufacturingmethod according to claim 12, wherein the D1 is set to be the outerdiameter of the screw or the valley diameter of the screw.
 15. The screwmanufacturing method according to claim 13, wherein the D1 is set to bethe outer diameter of the screw or the valley diameter of the screw. 16.A screw manufacturing method for manufacturing a worm screw, the methodusing: an annular cutter member that has a plurality of inserts radiallyarranged and is rotatable on its rotation axis; and a holding portionthat holds a work piece for forming the worm screw and is rotatable, thecutter member being inclined with respect to an axial center of the workpiece at a predetermined angle (mount angle), the method comprising astep of calculating the mount angle by formulae (1), (2), (3), (4) and(5) below, when a lead angle of the worm screw is different from themount angle:mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3){(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5) where D1≠0, ΔT≠0, and nindicates a number of threads.
 17. The screw manufacturing methodaccording to claim 16, wherein the ΔT is set to be within ranges offormulae (6) and (7) below: in case ΔT>0,{(screw outer diameter−screw valley diameter)/2}×0.6≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}  (6) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}×0.6  (7).
 18. The screw manufacturingmethod according to claim 16, wherein the D1 is set to be the outerdiameter of the screw or the valley diameter of the screw.
 19. The screwmanufacturing method according to claim 17, wherein the D1 is set to bethe outer diameter of the screw or the valley diameter of the screw. 20.A screw manufacturing method for manufacturing a metric screw thread,the method using: an annular cutter member that has a plurality ofinserts radially arranged and is rotatable on its rotation axis; and aholding portion that holds a work piece for forming the metric screwthread and is rotatable, the cutter member being inclined with respectto an axial center of the work piece at a predetermined angle (mountangle), the method comprising a step of calculating the mount angle byformulae (1), (2) and (3) below, when a lead angle of the metric screwthread is different from the mount angle:mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) where D1≠0, ΔT≠0, andn indicates a number of threads.
 21. The screw manufacturing methodaccording to claim 20, wherein the ΔT is set to be within ranges offormulae (6) and (7) below: in case ΔT>0,−{(screw outer diameter−screw valley diameter)/2}×0.6≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}  (6) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}≦ΔT≦{(screw outerdiameter−screw valley diameter)/2}×0.6  (7).
 22. The screw manufacturingmethod according to claim 20, wherein the D1 is set to be the outerdiameter of the screw or the valley diameter of the screw.
 23. The screwmanufacturing method according to claim 21, wherein the D1 is set to bethe outer diameter of the screw or the valley diameter of the screw. 24.An annular whirling cutter rotatable on its rotation axis comprising aplurality of inserts radially arranged, wherein the whirling cutter isinclined with respect to an axial center of a work piece formanufacturing a medical screw at a predetermined angle (mount angle),and, in case that a lead angle of the medical screw is different fromthe mount angle, formulae (1), (2), (3), (4) and (5) below aresatisfied:mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) in case ΔT>0,{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5) where D1≠0, ΔT≠0, and nindicates a number of threads.
 25. An annular whirling cutter rotatableon its rotation axis comprising a plurality of inserts radiallyarranged, wherein the whirling cutter is inclined with respect to anaxial center of a work piece for manufacturing a worm screw at apredetermined angle (mount angle), and, in case that a lead angle of theworm screw is different from the mount angle, formulae (1), (2), (3),(4) and (5) below are satisfied:mount angle=tan⁻¹{n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) in case ΔT>0,−{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5) where D1≠0, ΔT≠0, and nindicates a number of threads.
 26. An annular whirling cutter rotatableon its rotation axis comprising a plurality of inserts radiallyarranged, wherein the whirling cutter is inclined with respect to anaxial center of a work piece for manufacturing a metric screw thread ata predetermined angle (mount angle), and, in case that a lead angle ofthe metric screw thread is different from the mount angle, formulae (1),(2) and (3) below are satisfied:mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) where D1≠0, ΔT≠0, andn indicates a number of threads.
 27. A screw manufacturing machinecomprising: an annular whirling cutter that has a plurality of insertsradially arranged and is rotatable on its rotation axis; and a mainspindle that coaxially holds a base of a work piece for manufacturing amedical screw and rotates the work piece, wherein the whirling cutter isinclined with respect to an axial center of the work piece at apredetermined angle (mount angle), and, in case that a lead angle of themedical screw is different from the mount angle, formulae (1), (2), (3),(4) and (5) below are satisfied:mount angle=tan⁻¹ {n×pitch/(π×D 1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) in case ΔT>0,{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5) where D1≠0, ΔT≠0, and nindicates a number of threads.
 28. A screw manufacturing machinecomprising: an annular whirling cutter that has a plurality of insertsradially arranged and is rotatable on its rotation axis; and a mainspindle that coaxially holds a base of a work piece for manufacturing aworm screw and rotates the work piece, wherein the whirling cutter isinclined with respect to an axial center of the work piece at apredetermined angle (mount angle), and, in case that a lead angle of theworm screw is different from the mount angle, formulae (1), (2), (3),(4) and (5) below are satisfied:mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) in case ΔT>0,{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outerdiameter−screw valley diameter)/2}  (4) in case ΔT<0,−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outerdiameter−screw valley diameter)/2}×0.2  (5) where D1≠0, ΔT≠0, and nindicates a number of threads.
 29. A screw manufacturing machinecomprising: an annular whirling cutter that has a plurality of insertsradially arranged and is rotatable on its rotation axis; and a mainspindle that coaxially holds a base of a work piece for manufacturing ametric screw thread and rotates the work piece, wherein the whirlingcutter is inclined with respect to an axial center of the work piece ata predetermined angle (mount angle), and, in case that a lead angle ofthe metric screw thread is different from the mount angle, formulae (1),(2) and (3) below are satisfied:mount angle=tan⁻¹ {n×pitch/(π×D1)}  (1)D1={(screw valley diameter+screw outer diameter)/2}+ΔT  (2)screw valley diameter≦D1≦screw outer diameter  (3) where D1≠0, ΔT≠0, andn indicates a number of threads.